Multiple lines of evidence suggest the persistence of the Ivory‐billed Woodpecker (Campephilus principalis) in Louisiana

Abstract The history of the decline of the Ivory‐billed Woodpecker is long and complex, but the status of the species since 1944, when the last widely accepted sighting in continental North America occurred, is particularly controversial. Reports of Ivory‐billed Woodpeckers have continued, but none has reached the threshold of quality for general acceptance by ornithologists or the birdwatching public. In 2021, the U.S. Fish and Wildlife Service opened for public comment a proposal to declare the species extinct. Here, we present evidence suggesting the presence of the Ivory‐billed Woodpecker at our study site, based on a variety of data collected over a 10‐year search period, 2012–2022. These data are drawn from visual observations, ~70,000 h of recordings by 80–100 acoustic recording units, ~472,550 camera‐hours by as many as 34 trail cameras, and ~1089 h of video drawn from ~3265 drone flights. Using multiple lines of evidence, the data suggest intermittent but repeated presence of multiple individual birds with field marks and behaviors consistent with those of Ivory‐billed Woodpeckers. Data indicate repeated reuse of foraging sites and core habitat. Our findings, and the inferences drawn from them, suggest that not all is lost for the Ivory‐billed Woodpecker, and that it is clearly premature for the species to be declared extinct.

Cuba currently treated as a subspecies, C. p. bairdii (Jackson, 2002) or distinct species (Fleischer et al., 2006). Evidence suggests that the Ivorybill was widespread and perhaps very locally common, moving among ephemeral and widely dispersed areas of optimal habitat with access to recent burns, blowdowns, hurricane destructions, and other areas where the birds foraged, particularly on beetle larvae in dying or recently dead trees (Jackson, 2002).
The Ivorybill was severely impacted by collectors, hunters, and the cutting of bottomland forests and vast expanses of virgin pine forests in the U.S. (Jackson, 2004;Snyder, 2007). By the late 1930s, a documented population count of three territories was known from the Singer Tract, near Tallulah, Louisiana, while a range-wide search in continental North America resulted in an estimated population of 22 individuals in Florida, South Carolina, and Louisiana (Tanner, 1942), although no additional birds were seen.
The last widely accepted sighting of an Ivory-billed Woodpecker in North America was in 1944 at the Singer Tract (Hoose, 2004), where Tanner (1940Tanner ( , 1942 had studied the species. Reports of Ivory-billed Woodpeckers continued, however, with authorities estimating as many as 200 sightings after 1944 (Mendenhall, 2005;USFWS, 2010). Many of these reports were from less well-known sources, but some were from game wardens, field biologists, and ornithologists. Some observations also included physical evidence, such as photographs, audio recordings, videos, and a feather (Agey & Heinzmann, 1971;Collins, 2017;Lewis, 1988;Lowery, 1974;USFWS, 2010). In 2005, a highly publicized description of seven independent sightings and a video of a possible Ivory-billed Woodpecker in Arkansas was published (Fitzpatrick et al., 2005). But the identification and the continued existence of the species were strongly debated (Collinson, 2007; Jr., Gallagher, Harrison, et al., 2006; Jr., Gotelli et al., 2012;Haney, 2021;Jackson, 2006Jackson, , 2010Sibley et al., 2006;Solow et al., 2012). A follow-up, 2-year search did not produce additional imagery or documentation widely considered conclusive despite at least 15 reported visual sightings (Fitzpatrick, Lammertink, Luneau Jr., Gallagher, Harrison, et al., 2006;. Most recently, published evidence suggested that Ivory-billed Woodpeckers were present in the forests along Florida's Choctawhatchee River (Hill et al., 2006), and a morphometric analysis of a 2010 photo pointed towards an Ivorybill in Louisiana (Luneau, 2021).
None of the published reports and evidence over recent decades resulted in general acceptance that the species persisted anywhere in continental North America (USFWS, 2019), and in 2021, the U.S.
Fish and Wildlife Service opened for public comment a proposal to declare the species extinct (USFWS, 2021). Objections to conclusions of the continued existence of the Ivory-billed Woodpecker among scientists, elements of the birdwatching community, and public media have often focused on two key issues. First, the quality of all reports is so poor that they do not offer decisive proof of a living Ivory-billed Woodpecker (Hayes & Hayes, 2007;Jackson, 2006;McKelvey et al., 2008;Sibley, 2007). It has been argued that a rare bird needs to be documented with a higher standard of evidence and a greater threshold of physical support than routinely adopted for other species; the USFWS (2021) defined the objective evidence needed to verify the continued existence of the species as "clear photographs, feathers of demonstrated recent origin, specimens, etc." A second issue in consideration of the persistence of Ivorybills has been the lack of repeatability of observations (Sibley, 2007). The assumption is that if a rare resident species is found, then it should be repeatedly relocated, and that if it is not relocated, then the original observation or record is inadequate to prove persistence.
Here, we draw on 10 years of search effort to address the question of whether Ivory-billed Woodpeckers might persist in our Louisiana study site. We provide multiple lines of evidence, including visual observations, audio files, trail camera photographs, and drone videos, with evidence suggesting the intermittent but repeated presence of multiple individual birds with field marks and behaviors consistent with those of Ivory-billed Woodpeckers.

| MATERIAL S AND ME THODS
Our field research took place in bottomland hardwood forests in Louisiana from 2012 to 2022. Because of the endangered status of the species and ongoing research concerns, we omit specific location details. The search area was defined by mature bottomland forest habitat, previous visual sightings or aural data, and accessibility.
The area is a >90 km 2 mosaic of wooded swamp and bottomlands Field observations and data reported here were collected through visual encounters, audio detections, the deployment of trail cameras, and the use of drones to record videos. Most fieldwork was concentrated in the October-May period thought to encompass the breeding season of this species (Jackson, 2002).

| Visual encounters
Observational techniques that resulted in visual encounters included slowly moving reconnaissance, sitting in place with a view of appropriate habitat, and stakeouts of key areas, points, or cavities where we had seen or heard indications of the possible presence of Ivory-billed Woodpeckers. No standard protocol was followed for any of these observational techniques, but we were guided by local conditions, and observer experience and availability. Boats were not used due to the number and variety of obstructions in the water, reduced mobility, and inability to also handle recording and other equipment. Field observations focused on the birds occurring in this habitat. Although we carefully noted foraging sign (extensive removal or "scaling" of bark) and potential nesting or roosting cavities, we used these signs to focus our search strategy; we did not quantify or otherwise measure these Ivorybill signs and do not further report on them here.

| Audio recordings
From February to April 2019, and December 2019 to April 2020, we deployed AudioMoth acoustic recording units (ARUs; https://www. opena coust icdev ices.info/audio moth). Our goal was to use these recordings, machine learning, and open-source software to identify putative, nasal "kent" calls of Ivory-billed Woodpeckers, and to use the distribution of calls to narrow the search area for locating a nest.
Each ARU was placed in a waterproof plastic bag with a desiccant to absorb condensation, and attached to a tree at breast height with a tension strap. ARUs were deployed at ~200-m intervals across a predetermined grid pattern in the core of our research area and were programmed to operate from before sunrise to 1100, and 1600 to sunset.
In addition, field observers opportunistically recorded possible kent calls, as well as "double-knocks." Double-knocks are hard raps or blows, with the second note sounding like an immediate echo of the first (Tanner, 1942); double-knocks are characteristic of all Campephilus species (Jackson, 2002) and have been reported for Ivorybills (Tanner, 1942). Our recordings were made using handheld devices including Zoom H1 and Zoom H4N; the frequency of encounters was not noted.
Audiospectrograms of selected calls and double-knocks were prepared using Raven Pro software, Version 1.6.4. Results were compared with audiospectrograms prepared with the same software of known Ivory-billed Woodpeckers recorded by A. Allen and P. Kellogg in the Singer Tract in April 1935 (the "Singer recordings"), and to recordings made by J. Dennis in February 1968 in the Big Thicket of Texas (the "Dennis recordings"). The Dennis recordings are assumed to be of an Ivorybill by the Macaulay Library (Cornell Laboratory of Ornithology), although the bird was not seen while recorded, and some ornithologists differ in their opinions as to the identity of the vocalizing bird.

| Trail camera imagery
We used trail cameras in an attempt to capture images of Ivory- We placed trail cameras strategically at sites where we noted the presence of (a) tight-barked trees that appeared to have been scaled, (b) trees that were damaged or in poor health and expected to die, or (c) upright or fallen trees of species that are known to be favored for feeding by Ivorybills. Our best results, however, followed placements made when informed by visual or aural encounters with suspected Ivorybills. Cameras trained to capture images of birds foraging in the mid to upper canopy relied on time-lapse programming at intervals of 5-60 s, while those targeting lower portions of trunks or fallen branches were usually set to a motionsensitive setting. Most often, a single trail camera was placed in position to capture activity at a tree, but in some cases, especially where suspected activity had been captured, 2-4 cameras would be placed. This permitted a focus on more sides of the tree, and by programming each camera to different time blocks, we could better avoid taking photos into the sun. Batteries and SD cards were changed as needed or when possible.
No manipulations were made to trail camera images other than adjusting contrast and brightness to the entire image using Photoshop or Apple Photos; there was no attempt to alter the appearance of individual subject birds. GlueMotion software was used to compile still images from trail cameras into time-lapse videos.

| Drone videos
Because we recognized that Ivory-billed Woodpeckers regularly fly through and over the canopy (Tanner, 1942), and drones have been shown to be effective in detecting putative Ivorybills (Collins, 2018), we hovered a drone in place well above the forest, passively filming the treetops to record birds flying within view of the onboard camera. Hovering the drone at a high altitude, just below the Federal Aviation Administration's maximum height of 122 m (400 ft), minimizes disturbance to birds and other wildlife (Duporge et al., 2021;Weston et al., 2020), and creates a relatively stable platform for the camera that results in less blurring of video images than if the drone were moving.
Selection of flight and video locations was informed by many factors, including available habitat, the configuration of habitat on a landscape scale, accessibility of launch sites, permit requirements, and most critically, our history of aural detections and sightings of putative Ivorybills, and locations of possible foraging signs and cavities. Flights were made primarily near dawn and in the morning hours directly to preselected points where the drone remained in place as long as batteries permitted. Videos were filmed at a shallow (oblique) angle that included treetops up to 800 m away, allowing for a wider field of view and increased opportunity for an encounter with a woodpecker as compared to a directly downward (nadir) view.
Flights during 2019 were made with a DJI Mavic 2 Zoom filming with a 4 K camera, often using the 2× optical zoom lens. In spring of 2020, we began using the Autel Evo II drone with swappable 6 K and 8 K cameras. Due to a smaller sensor, the 8 K camera did not perform well in low light level conditions such as during early morning and on cloudy days, so most videos were recorded with the 6 K camera.
Postprocessing of drone videos was minimal; we first cropped the videos using a cropping software (Clideo.com), then we extracted stills using an extraction software (SnapMotion).

| Visual encounters
Skilled, reliable observers associated with our team, all abundantly familiar with Pileated Woodpecker, Red-headed Woodpecker (Melanerpes erythrocephalus), and other birds of the area, reported 16 visual observations deemed by the observer to be probable Ivory-billed Woodpeckers. Seven of these were of high enough quality that the observer considered the sighting to be definite (See Appendix 1). Although these observations lack photographic verification, many are supported by field drawings. Most observers reported birds in flight with prominent white trailing edges to the wings, or a large bird with a prominent white "saddle" across the lower back (formed by the white trailing edges of the wings when folded across the posterior dorsum) clinging to a tree in the characteristic style of a woodpecker. Nearly every observer noted unique, brilliant white plumage, unlike anything seen in any other black and white bird. Most observers had an instant reaction to their sighting, dominated by astonishment at seeing a bird clearly different from any other, and manifested in the realization that in a sharp and focused manner, they needed to record every detail of the experience.

| Audio recordings
From February to April 2019, and December 2019 to April 2020, we deployed 80-100 AudioMoth ARUs resulting in ~70,000 h of recordings. The large volume of recordings, and issues encountered in using the "Singer recordings" as a template for machine learning, proved impractical. We were unable to produce distributions of kent calls to narrow the search area for locating a nest. Data derived from AudioMoth recordings will be further analyzed and discussed in a future paper.
Possible kent calls and double-knocks were also heard at infrequent intervals and recorded opportunistically in our study area.
We did not quantify the number of each, or score or rank each according to our confidence in identification as putative Ivorybill audio, but possible double-knocks were heard far more frequently than putative kent calls. We present here examples from recordings of a series of kent-like calls and double-knocks (See Appendix 2) and display audiospectrograms (Figures 1-3 All kent calls in Figure 1 show a series of equally spaced partials. The nasal quality of the kent call arises when most of the sound energy is in the third or higher partial (Pieplow, 2017). In the Courtman recordings from our study site (Figure 1n-q), the third partial is consistently the strongest, and in the 3-h Courtman recordings (not fully published here), the third partial, at ~1750 Hz, is frequently the only feature visible on the audiospectrogram. In comparison, on the Dennis recordings (Figure 1i-m), the third partial, at about the same frequency as that in the Courtman recordings, is as strong as or slightly weaker than the fourth partial. By contrast, in the Singer recordings ( Figure 1a-h), the strongest partial varies from the third to the fifth, and there are frequently 2-4 more or less equally strong partials. The frequency of the third partials on the Singer recordings varies from ~1600 to 2050 Hz. Like the Courtman recordings, the Singer and Dennis recordings share the (mostly) weaker second partial compared with the fundamental. Two characteristics are often mentioned in determining whether a double-knock can be assigned to an Ivory-billed Woodpecker: The time interval between the first and second knock is generally 60-120 ms (BWCP, 2019;Hill et al., 2006), and the first knock is generally louder than the second (Jackson, 2002;Tanner, 1942).

| Trail camera imagery
We simultaneously deployed 6-34 trail cameras resulting in ~472,550 camera-hours of activity. An important series of trail camera photos followed our sighting of an apparent Ivory-billed Woodpecker landing at ~40 m distance from the observer in a live but declining sweetgum tree on October 27, 2019 (encounter described in Appendix 1).
Trail cameras, nearly continuously deployed on this tree since then,  (Bock & Miller, 1959;see below), and be characteristic of that species. While the image quality is too poor for precise measurement, the relatively long neck aspect ratio, proposed as characteristic of the Ivorybill (Luneau, 2021), is also highly suggestive, and evident as distinct from Pileated Woodpeckers in many of F I G U R E 1 Audiospectrograms of recorded sounds: (a-h) calls extracted from ML6784 recorded by A. Allen and P. Kellogg in the Singer Tract in April 1935 and known to be Ivory-billed Woodpeckers (the Singer recordings); (i-m) calls extracted from ML104395 recorded by J. Dennis in the Big Thicket, TX, in February 1968 and assumed to be an Ivorybill, although the birds were not seen while recorded (the the photographs taken in the 1930s by Allen and Kellogg (1937) and Tanner (1942).
In Figure 6, we compare the putative Ivory-billed Woodpecker photograph from Figure 5 to one of a known Ivory-billed Woodpecker from the Cuban population (Gallagher, 2007) that was also photographed at a considerable distance. The remarkable similarities in the images include the angle of the bird to the bole of the tree, the size and shape of the white saddle, and the shape of the crest.   is present in many frames. Most intriguing is that birds in these images appear to have a characteristic body posture resulting from the distinctive morphological adaptations of the feet and legs of Campephilus woodpeckers as compared with Dryocopus woodpeckers like the Pileated Woodpecker (Bock & Miller, 1959). The Pileated is one of the most unspecialized of the truly arboreal woodpeckers, and when perched on a tree trunk, the legs are positioned more or less beneath the pelvic girdle, the joints are fully flexed, and the tarsi are held well away from the tree trunk.
By contrast, the Campephilus woodpeckers are characterized by pamprodactyly, a pedal morphology that enables the facultative forward rotation of all four toes (Bock & Miller, 1959). One result of this specialized modification in the structure of the toes of the highly arboreal Ivory-billed Woodpecker is seen in the position of the legs.
The feet and legs are held outward from the body and are directed diagonally upward and sidewise ( Figure 8), with both feet wide apart and more anterior relative to the body than seen in other woodpeckers (Bock & Miller, 1959;Tanner, 1940). Usually, the angle between the tarsi and the horizontal plane is ≤45°, and the tarsi often seem to be pressed against the tree trunk. The stance of the Ivorybill generally results then in a more obtuse angle of the intertarsal joint (where the leg bends between the tibiotarsus and the tarsometatarsus) and is evidence of the more efficient scansorial adaptations of the Ivorybilled Woodpecker compared with the Pileated Woodpecker (Bock & Miller, 1959). This obtuse angle of the intertarsal joint is often visible from a distance and can result in the wider angle of the Ivorybill's back to the bole of the tree than that typically seen in Pileated Woodpeckers. Combined with feet extended diagonally upward and to the side of the body, this stance is readily seen in our comparison of images of known Campephilus woodpeckers (Figures 6a and 8b,c), and in our images of putative Ivorybills (Figures 6b and 8a,d).
One of the photo sequences we find most compelling, however, was obtained on November 30, 2019. These trail camera photos involve what appears to be a foraging family group. When viewed in succession (See Appendix 3), the resulting "video" clip appears to show three large, crested woodpeckers moving and foraging together. The "video" is composed of individual trail camera photographs taken automatically every 5 s. Although distance and lighting are difficult, a white saddle can be clearly seen in multiple frames, including a frame extracted and reproduced in Figure 4 (top) showing a woodpecker with a prominent white saddle on the lower part of the folded wings. We note also the proximity of the three birds to one another in the "video," and their foraging behavior, including movements throughout the tree: on the bole and major branches, and even on smaller branches. Foraging appears to be very active and even acrobatic at times, with birds clinging to the tops, sides, and undersides of the branches. We recorded very similar foraging behavior by at least two birds possessing white saddles on the same tree on October 12, 2021, with very active and acrobatic movements across the tree, including smaller branches (See Appendix 4).

| Drone videos
We used drones to document the possible presence of Ivory-billed Woodpeckers at our study site. We made ~3265 drone flights and

in).
A very similar set of videos (Appendices 9 and 10) was filmed on October 20, 2022, with the critical difference being that this video includes two birds sharing very similar plumage characteristics consistent with that of Ivory-billed Woodpeckers. These two birds are clearly interacting, although the video lacks the definition to determine whether they may be a male-female pair or perhaps a parentoffspring pair.
The large size of the birds in Appendices 9 and 10 is indicated again, this time with the presence of a comparably small Red-headed Woodpecker just prior to the arrival of the putative Ivorybills. In Appendix 9, the video appears at full speed. At 7.5 s, a Red-headed Woodpecker flies from the lower-right to the lower-middle foreground, briefly lands, and then flies off in the direction from which F I G U R E 5 Composite figure comparing the size of three species of woodpeckers to the apparent Ivory-billed Woodpecker. Inset species were photographed on the same tree, with the same camera in the same place but at different times. These three images were extracted from their original frames and placed as insets on a fourth frame that shows the presumed Ivorybill on October 1, 2021. All woodpeckers here are depicted at the same scale in their original, unedited size. Arrows point to the location of where each bird was located on the tree. Insets include an unidentified small woodpecker (top), a Pileated Woodpecker (middle), and a Red-headed Woodpecker (bottom). The presumed Ivory-billed Woodpecker is circled in white without an arrow.
it arrived. The Red-headed Woodpecker is identified by its small size, and the dorsal surface of the wings shows a black leading edge with extensive white, but the white is continuous from wingto-wing because of the presence of the prominent white rump.
Beginning at 34 s, two putative Ivory-billed Woodpeckers enter the frame from the mid-right margin. These two birds, clearly interacting, display field marks consistent with Ivory-billed Woodpeckers, including the dorsal wing surfaces with a black leading edge, and extensive white trailing edge divided by a prominent black body. A portion of this video is cropped and slowed to three-quarter speed in Appendix 10.
Finally, we offer images ( Figure 10 ists. The Singer recordings, however, present their own limitations as the standard for identifying Ivorybills by call (Hill et al., 2006).
These recordings were made with a parabolic microphone that can introduce subtle acoustic distortions (Bruyninckx, 2018). In addition, the recordists were standing near the base of the nesting tree; the birds were agitated and it is reasonable to assume that a bird under extreme stress from the nearby presence of observers may call in unique ways. In fact, Tanner (1942) commented on the variation in calls of Ivory-billed Woodpeckers, writing that, "The kent note, given in a monotone, and slowly or infrequently, is the ordinary call note.
When the bird is disturbed, the pitch of the kent rises, and it is repeated more rapidly, frequently doubled…" This description of the ordinary note more closely resembles the Courtman and Dennis recordings than the Singer recordings.
In addition, variability among recordings may be a result of differences in habitat or landscapes. Sound propagation from the nest to the recording microphone on the ground nearby, as in the Singer recordings, will be very different from that through the forest, so F I G U R E 6 A side-by-side comparison of cropped photos from: (a) the unenhanced image of an Ivory-billed Woodpecker taken by George Lamb in Cuba in 1956 (Gallagher, 2007), and (b) the original, unretouched Project Principalis photo from Louisiana from October 1, 2021. Each photograph is also shown enlarged and further cropped below each original. These comparisons emphasize the similarities of appearance between the known Cuban Ivory-billed Woodpecker and the presumed Ivorybill from Louisiana where each image was obtained from ground level under challenging field conditions, as opposed to many existing photos of North American Ivorybills that were obtained from cavity-level blinds (Michaels et al., 2021;Tanner, 1942).
calls and their spectrograms may appear quite different in unique spaces (Morton, 1975;Wiley & Richards, 1978). More recordings, including experimental manipulations under a variety of conditions, however, would help clarify these and similar questions.
Complementing the audio evidence, the repeated appearance of large woodpeckers in photographs and videos with characteristics consistent with those of an Ivory-billed Woodpecker is also suggestive. We note that trail cameras, typically designed for close-range photography, are being used here to take photos at greater distances, and therefore many of our photographs remain ambiguous. For instance, some frames clearly show a white saddle consistent with that expected of an Ivory-billed Woodpecker, and in some cases, these field marks can be seen in successive or multiple frames. In other cases, however, successive frames may show no white visible for the same birds that showed white in earlier frames. Lighting conditions and position of the bird have been recognized as accounting for the near absence of white in some photos of known Ivory-billed Woodpeckers (Jackson, 2004), and the angle of the camera to the bird also affects the amount of white appearing in a photograph (Jackson, 2004;Michaels et al., 2021). In this case, we are shoot- Artifacts associated with a "white bleed" and a "black halo" can make it difficult to assess plumage coloration, and the halo effect may be enhanced when cropping distant images as this results in a loss of quality and more pronounced fringing distortions or chromatic aberrations. This may be especially problematic when trying to distinguish the relative position and size of white and black plumage on a flying bird. The flapping motion of the wings, the forward motion of the bird, and ambient or local shading can produce the illusion of greater amounts of white than actually present or a black halo around white patches. This is a particular concern in identifying putative Ivory-billed Woodpeckers in flight when the amount of white in the wing, and the presence of black on the leading edge and white on the trailing edge of the wing is a critical field mark.
Artifacts associated with camera quality, however, are far less of an issue with recent HD video technology and should be of much less significance in evaluating video shot in 4 K or 6 K HD as we do.
In addition, in multiple videos presented here, we see the same plumage patterns, especially when the bird is swooping up to land, or initiating flight bounding when active flapping ceases. In these videos, too, the diagnostic white saddle formed by the white trailing edge of the wing appears after the individual has landed and is stationary on the tree, even under various light conditions. This is a strong indication that the apparent white trailing edge of the wing is not an aberration. Finally, as seen in Appendices 11 and 12, our drone videos were also able to capture Pileated (See Appendix 11) and Red-headed (See Appendix 12) woodpeckers in similar landing flights. In these videos, aberrations are not an issue, the distribution and extent of black and white plumage is as might be expected for these species and is very unlike that of the presumed Ivory-billed Woodpeckers.
The variety of evidence we have gathered over many years indicates repeated re-use of foraging sites and core habitats and offers unusual repeatability of detections of putative Ivory-billed Woodpeckers. The lack of repeatability of observations has been raised in the past to dismiss purported Ivorybill sightings. For example, countering claims around the Luneau video from Arkansas, critics suggested that, "experience with other rare birds, especially resident species, suggests that any valid sighting should very quickly lead to more sightings" (Sibley, 2007). This criticism was lodged, despite the fact that the Luneau video followed a series of sightings and was itself followed by additional sightings and acoustic recordings (Fitzpatrick et al., 2005). Repeatability in our observations is seen at a variety of scales. All of the observations reported here took place in a single forested block and a single watershed. Almost all of the encounters reported here occurred within 1.6 km of one another; the majority of the best trail camera photos were taken over two, 3month periods on the same tree; and drone videos were taken over a several-year period.
Our trail camera "videos" and drone videos of evidently socially bonded and very active foraging by two and three large, crested Ivorybills reportedly show no indication of being strongly territorial (Tanner, 1942). In the Singer Tract, home ranges did not appear to be defended during the breeding season, and wandering birds that were encountered seemed to be tolerated by resident birds.
In addition, Sonny Boy, the male offspring that Tanner banded in 1937, remained with his family group for a full 2 years after fledging (Michaels et al., 2021). By contrast, the Pileated Woodpecker generally appears to be territorial year-round, only tolerating birds from other territories at distances of >100 m (Bull & Jackson, 1995). Adult Pileateds typically drive young away from the territory in the fall, often as early as September, but anecdotal reports do exist of three Pileateds together during winter months (Bull & Jackson, 1995). Our observations of three birds appearing just a few meters apart (See Appendix 3), well after a presumed fledging period and for an extended time, is more consistent with an Ivorybill family group than an unusual Pileated or mixed-species group but should not be considered definitive. However, considering that we see white on the wings of birds in successive frames (Figure 4), even at a considerable distance and under poor lighting conditions, is consistent with these sequences including Ivory-billed Woodpeckers.
In addition to the evidence of a family group, the observed foraging behavior is distinctly unlike that of a Pileated Woodpecker.
Pileateds select large-diameter trees (Bull & Jackson, 1995;Newell et al., 2009), and dead trees are used out of proportion to availability (Newell et al., 2009). Large rectangular excavations are characteristic; these can be >30 cm in length (Bull & Jackson, 1995). Although Pileateds may also glean and peck, their bark scaling behavior is a distinctly uncommon activity in Louisiana bottomlands (Newell et al., 2009). Pileated Woodpecker foraging tactics are rather slow and methodical, and concentrated on the bole and major branches of large trees, as the species avoids trees in smaller size classes (Newell et al., 2009). The foraging style of the Ivory-billed Woodpecker seems to be largely undescribed, other than the importance of scaling of the bark of hardwoods (Tanner, 1942). It is unclear from the literature whether foraging as active as we document is typical of Ivorybills, but our subsequent careful inspection of the smaller branches of the tree where the putative Ivorybills were photographed did reveal extensive scaling of even the smaller branches in the canopy. Furthermore, photographs taken by Tanner in 1939 similarly reveal a group of three Ivorybills foraging together on a tree at the same time, while also documenting that the three birds were also less than 1 m apart from one another (Michaels et al., 2021).
Such active foraging behavior would be enabled in the Ivorybilled Woodpecker by the unique foot function resulting from the pamprodactyl condition allowing the acrobatic hanging while foraging. This might be the case because when the bird is climbing on smaller limbs, the feet can encircle the limb and thus obtain better support (Bock & Miller, 1959); however, functional studies and com- In addition to foraging behavior, flight characteristics may also be used to aid the identification of these birds. High speed and direct flight were previously noted in the Ivory-billed Woodpecker (Allen & Kellogg, 1937;Tanner, 1942), and may be similar to that seen in the putative Ivorybill in Appendices 5 and 6. By contrast, Pileated Woodpecker flight is characterized as "rather slow, but vigorous and direct" (Bull & Jackson, 1995). Flight bounding is also known from the Pileated Woodpecker but is not mentioned in the historical literature of the Ivory-billed Woodpecker (Collins, 2011). We suggest that our observations help explain the twin problems of why the Ivory-billed Woodpecker has been so difficult to detect and to relocate or re-encounter over the past 80 years.
Assuming that this species does still exist, it is obviously extraordinarily rare. Historical reports suggest that the Ivory-billed Woodpecker was always scarce (Jackson, 2002), and famously vagile and unpredictable. It was known to colonize or utilize rich but ephemeral resources associated with recent burns, hurricane blowdowns, and floodwaters where dying or recently dead trees hosted favored beetle larvae (Jackson, 2002). This likely helps to explain the unusual mobility of the species that have contributed to the difficulty in locating and re-encountering the species. This may explain, too, the apparent ~2-year gap in foraging on one of our nearly continuously monitored trees, supporting the reported intermittency in woodpecker movements, and likely, the phenology of prey. Continued, long-term monitoring of trees utilized by putative Ivorybills is warranted to better understand woodpecker movement and foraging patterns.
Difficulties in detecting and relocating putative Ivorybills hinge, however, on the misperception that, if present, the Ivorybill is F I G U R E 1 0 Images extracted from drone video clips, all filmed at our Louisiana study site, depicting landings on upright snags by three woodpeckers: (a) Pileated Woodpecker, (b) putative Ivorybilled Woodpecker, and (c) Red-headed Woodpecker. Images have been cropped and sized for comparative purposes but otherwise have not been manipulated. The full video clips of these landings are available in Appendix 7 (putative Ivory-billed Woodpecker), Appendix 11 (Pileated Woodpecker), and Appendix 12 (Red-headed Woodpecker). Here, the Pileated Woodpecker (a) displays a very small amount of white on the dorsal surface of the wings. In (b), the dorsal wing surfaces of the putative Ivorybill show extensive white divided by a prominent black body, and a black leading edge to the wing. In (c), the dorsal wing surfaces of the Red-headed Woodpecker also show a black leading edge to the wing with extensive white, but the white is continuous from wing-to-wing because of the presence of the prominent white rump.
relatively easy to find-a misperception that extends at least as far back as Tanner (Tanner, 1942). Tanner was a meticulous observer, but he apparently never located an Ivory-billed Woodpecker outside the Singer Tract, despite his numerous searches throughout the southeast (Bales, 2010;Tanner, 1942). Tanner (1942) noted that "the difficulty of finding the birds, even when their whereabouts was known … limited the number of observations." Nonetheless, the misperception emerged, sometimes fueled by Tanner himself, that the Ivorybill was noisy and easy to find. However, this view was largely based on a single noisy family group that was annoyed with the human intruders below their nest and therefore easily recorded by Tanner and Allen (Tanner, 2001).
Misperceptions on the ease of finding the Ivorybill extend to the frequent argument that, in the modern era, it is unlikely that a large, distinctive woodpecker could escape the sights, cameras, and recorders of birdwatchers and other people who recreate or work outdoors in remote areas (Kaufman, 2020;Roberts et al., 2010;Sykes, 2016). Even with the popularity of birdwatching, however, to four miles or more in diameter (Tanner, 1942). Ivorybills have also been reported to wander over even greater distances and to cross cutover and otherwise unsuitable habitat (Lamb, 1957;Tanner, 1942).
Data presented here of putative Ivory-billed Woodpeckers support evidence that the species moves widely among dispersed areas of optimal habitat with ephemeral resources occurring in dying or recently dead trees (Jackson, 2002).

| CON CLUS ION
We conclude that multiple lines of compelling evidence suggest that Ivory-billed Woodpeckers persist in our Louisiana study site.
Cumulatively, our visual observations, audio files, trail camera photographs, and drone videos, suggest the intermittent but repeated presence of multiple individual birds with field marks and behaviors consistent with those of Ivory-billed Woodpeckers.
The habitat conditions described above apply to many places in the American Southeast (USFWS, 2010). If the Ivory-billed Woodpecker continues to survive in Louisiana, this has conservation management implications not only in that state but also widely within the historic range of the species. We expect that Ivorybills persist in some of these other places also, if not permanently then episodically. Their numbers cannot be expected to improve unless many more large and continuous bottomland hardwood forests are actively or passively managed to exhibit old growth characteristics.
Forested tracts must be large enough and numerous enough that ecological changes caused by natural catastrophic events, such as fires (Bedel et al., 2013), and floods or hurricanes (Doyle et al., 1995;Faulkner et al., 2007), will allow surviving Ivory-billed Woodpeckers opportunities for a diversity of habitats, including mature bottomland hardwoods. The quantity and distribution of habitat must also take into account changes wrought by anthropogenic climate change and its effects on hydrology, moisture and drying cycles, and severe storm events. Only then, can there be an expectation of a larger number of populations or subpopulations of this iconic species.
The report contained here is not the end of our efforts. We are encouraged and energized by what we have discovered and accomplished. We are optimistic that technologies will continue to improve our outcomes, including documentation through environmental DNA and other physical evidence. We believe that our intentional and systematic survey design is paying off through complementary lines of investigation. Our findings begin to tell a larger story not just of whether the Ivory-billed Woodpecker persists in Louisiana, but how it has survived and why its survival has been so difficult to document. Finally, we also believe that our methodologies can be translated to other sites, thus offering opportunities for additional documentation of the species. Our findings, and the inferences drawn from them, suggest that all is not lost for the Ivory-billed Woodpecker and that it is clearly premature for the species to be declared extinct.

CO N FLI C T O F I NTE R E S T S TATE M E NT
The authors declare no conflicts of interest.

DATA AVA I L A B I L I T Y S TAT E M E N T
The authors confirm that all of the data supporting the findings of this study are available within the article and its appendices.

Visual encounters
The following are first-hand reports of apparent Ivory-billed Woodpeckers in our search area. Our team reported 16 visual observations of probable Ivory-billed Woodpeckers, seven of which were of high enough quality that the observer considered the sighting to be definite. Those seven are described here. One (by Frank Wiley) occurred in 2015, before consistent fieldwork was initiated, but it is included here for its quality and for completeness.

From Frank Wiley, co-founder of Project Coyote (now deceased; as re-told by Mark Michaels)
On April 3, 2015, Frank and I hiked into the area we called the "hot zone." We did some playbacks of Ivorybill kent calls at approximately 0800, although I did not record anything about them in my notes. We then proceeded walking in a more or less southerly direction with I did not notice the head of the bird, perhaps because the bird was flying away from me, but I did not see any red. I did not see the shape of the tail but it was black, or at least dark, otherwise I believe I would have noted its whiteness. I did not see the ventral area as the bird was flying directly away from me and angled upwards ( Figure B1).

From Don Scheifler
It Looking at my photograph later, I was able to find what appeared to be the body of a bird in the fork of the tree, with the head apparently obscured. What is visible appears to include a white patch on the bird's lower back-a major field mark for identifying Ivorybills.
The photograph is poor and will not be considered conclusive by itself, but it confirms to me that the bird I saw in flight that day was an Ivory-billed Woodpecker ( Figures C1 and D1).

From Peggy L. Shrum
From my field notes of February 8, 2020, I described the following: On the trail at 0615 to (an undisclosed area) with Erik Hendrickson.
We were attempting to reach and replace all of the ARUs (acoustic recording units) in the area, but as always, this area's terrain was rough and we were moving slowly. By around 0900 we had only reached the third ARU. We were on our way to the fourth, passing F I G U R E B 1 Field drawing by S. C. Latta of the bird he encountered on February 10, 2019.
through large areas of standing water, with lots of backtracking and re-orienting ourselves. As we slowly proceeded to the fourth point, I saw a large bird on a fallen log. I stopped; Erik was beside me to my right.
I whispered, "What is that?" The bird was roughly 20-25 m ahead of us, and oriented facing our right. The head was obscured by vegetation, and the body was visible from the chest and back. My first impression was that I was F I G U R E C 1 Cell phone capture of possible Ivory-billed Woodpecker at upper center (circled in red), obtained in conjunction with sighting on October 27, 2019.

F I G U R E D 1
At left, a cropped and enlarged version of the same photograph appearing in Figure C1. The red arrow points to the white saddle on the bird's lower back, with a shape very similar to those in historical Ivorybill photographs from 1935 of a male (center) and female (right). The central portion of the white saddle extends anteriorly leading toward faintly visible dorsal stripes in the photograph at left, similar to the historical photographs and significantly different from those of Red-headed Woodpeckers in which the central portion of the white saddle does not extend anteriorly. Historical photographs (male: ML72932681; female: ML72932701) by Arthur A. Allen, used by permission of Macaulay Library at the Cornell Lab of Ornithology seeing a black and white chicken, with black towards the front of body, and strikingly white plumage on the rear portion. No tail was visible.
As it began to sink in what I was looking at, I whispered to Erik, "I see the white." I then stepped to my left to use a large oak for cover as I also fumbled for my binoculars. Erik stepped to his right behind another tree.
The bird then flew a few feet back, clung to the trunk of a tree, and perched vertically, 5-6 ft off the ground in bright sunlight. I very clearly saw what I can best describe as a brilliantly white, "blunted heart" shape. That is, if you drew a valentine heart and blunted the top and bottom such that the two top curves as well as the bottom point were flattened; that is what I saw on this perched bird's folded wings.
I did not make out the head or tail. The bird cocked to its left with a jerky motion and re-oriented itself at an angle. It then flew and was gone instantly. I did not see the bird in flight, but I did see a burst of white as the bird-initiated flight, and I was able to make out the shape of the bird's left wing before it disappeared. The wing was long and pointed in shape, more like a high aspect ratio wing shape.
It was not at all rounded ( Figure E1).
We waited still and quiet for about 20 min but heard or saw nothing more. I immediately made field notes and sketches, and we measured off the distances and the diameter of the tree. We took a lot of photographs, and placed several trail cameras, as well as an ARU at the location. The cameras did not produce any images, and the ARU did not record any putative Ivorybill sounds. Looking ahead for a landmark, I looked across a clearing, and saw a blur of wings. The blur was at ground level, or just above the ground. The blur was mostly white-part of it was brilliant white, and other parts (smaller parts) faded to grayish white. The blur seemed to be overall spherical. It was obviously a bird, and the blur went powerfully upwards (I estimated at an 80° angle) into the leafless crown of a tree.

From Erik Hendrickson
I saw no field marks that we associate with Ivory-billed Woodpecker: I did not see the head, or bill, or neck or body, or the tail-it was just a powerful, spherical blur of white wings, launching powerfully in a near vertical ascent. It was startling to see, and I suspect I startled the bird. It seemed to me an amazing display of power.
It was larger and more powerful than any passerine, or any other bird I saw in the bottomland. It flew upward unlike any bird I have ever seen anywhere. It happened in a startling second.
None of my observations are considered "field marks." However, they identified the bird. I whisper-called for Peggy, and we stood behind a 1.2 m (4-ft) diameter oak. In the tree canopy ahead, I saw a large, "dark and light" bird fly from right to left, but I did not see F I G U R E E 1 Field notes from Peggy Shrum's observation on February 8, 2020.
where it flew from, or where it flew to, and I did not see any details of the bird. I saw the bird "move" through the canopy again in a shorter flight, and it was again completely obscured before and after the movement.
Peggy and I finally decided to move forward, she to the left and me to the right of the big oak. Within a minute or two, Peggy saw "movement"-enough to tell the bird had launched, and called out, "It's gone." I had participated in searches in this bottomland hardwood forest for a cumulative 12 weeks, specifically looking for birds, and seeing all of the expected species. Although it is always difficult to judge size and distance in the field, several hours after my observation I noted that the bird I saw with an unobstructed view was the size of (or slightly smaller than) a Red-shouldered Hawk, a very common species in our study area. I later determined that this puts my obser-  Before recording the above, I had yelled, "Ivorybill!" Not, "What was that?", "Did you see that?", or even "I think I saw one." It was an expression of shock and certainty.
The sighting lasted ~3 s. Skies were overcast, and no field marks were noted on a couple of Pileateds that had flown by previously.

A PPE N D I X 5
A half-speed video filmed by Autel Evo 2 6K drone on February 23, In a subsequent flight by the same bird appearing in Appendix 5, here shown at full speed, the presumed Ivory-billed Woodpecker flies across the lower foreground while flight bounding, including a remarkable upward bound, then spreads its wings as it prepares to land on an upright tree trunk allowing a full dorsal view (Video 6).

A PPE N D I X 7
A cropped view at half-speed of the landing seen in Appendix 6.
Readily visible features include extensive white on the dorsal surface of the wings, and a clear black body dividing the wings in all frames where it is visible. Upon landing, the putative Ivory-billed Woodpecker shows a clear white saddle across the lower back, even as it moves across the branch, disappears momentarily around the back side of the branch, and then reappears. Calculations appearing in Appendix 8 suggest that this bird has a wingspan of 74.7 ± 7.9 cm (29.4 ± 3 in) (Video 7).

A PPE N D I X 8
Calculating wingspan of a putative Ivory-billed Woodpecker from a drone video shot on February 23, 2021 in Louisiana 1. Using a mm ruler on a computer monitor (Dell SE2419H), we made three measurements of the bird's wingspan (WS) in four frames where the wings were judged to be fully extended (n = 12 measurements).
The measured frames were 8, 9, 10, and 11 frames prior to landing. In these four frames, the wingspan appeared maximum and uniform. Data from these measurements suggested that in frames 8 and 11 the wings are somewhat less fully spread, so these measurements were eliminated, and we calculated the mean of the six measurements from frames 9 and 10: Wingspan measurement = 14.9 mm Estimate of error of measurement = 0.5 mm Wingspan measurement = 14.9 ± 0.5 mm (±3.3%) 2. Using a mm ruler on the same monitor with the same frame and same zoom factor, we made three measurements of the DBH (diameter at breast height) of the tree. These measurements were: 14.5, 13.2, and 13.4 mm. We took the mean of these measurements.
DBH measurement = 13.7 mm Estimate of error of measurement error = 1 mm DBH measurement = 13.7 ± 1 mm (±7.3%) 3. Note that all measurements are for the random zoom factor used on the computer monitor in this particular instance; if repeated on this or any other computer monitor, the zoom factor will surely be different. What is important is the ratio of the wingspan to the DBH, not the absolute value of the measurements themselves.
The ratio of WS to DBH = 14.9/13.7 = 1.09 ± 0.1 (±10.6%) 4. Since actual DBH measured at the tree = 74 cm, our best preliminary estimate of WS (before taking into account the difference in distance from drone to bird, and drone to DBH point) is:

WS = (ratio of WS to DBH) (actual DBH)
= (1.09 ± 0.1) (74 cm) = 80.7 cm ± 8.5 cm = 31.8 in ± 3 in 5. However, the bird was slightly closer to the drone than the point on the trunk where the DBH was measured. To take into account this difference, we compared the distances from the drone to the bird, and the drone to the DBH point: To calculate the distance from the drone to the bird, we used the Pythagorean theorem, c 2 = a 2 + b 2 .
We knew the height of the drone was 350 ft (106.7 m), and the horizontal (along the ground) distance from the drone to the tree (and to the bird) was measured by a subsequent drone flight as 450

V I D E O 7 V I D E O 6
ft (137.2 m). We estimated that the bird was 80 ft (24.4 m) above ground based on prior estimates of tree heights in our search area.
We knew the height of the drone was 350 ft (106.7 m), and we estimated the horizontal distance from the drone to the tree (where DBH was measured at 130 cm = 4.25 ft above ground) was 450 ft (137.2 m) (as measured by a subsequent drone flight).
So: Distance, y, from drone to DBH is: f. The bird is 80 ft up in frames 9 and 10; g. The horizontal projected distance from drone to DBH point and to the bird are the same, where the "horizontal projected distance" is the part of the "distance" represented ONLY by the horizontal part. We calculated above the "actual" distance that lies along the hypotenuse of a "sloped" line of sight.

A PPE N D I X 9
A full speed video shot on October 20, 2022 with an Autel Evo II drone with a 6K camera. At ~6 s a Red-headed Woodpecker enters the middle foreground, briefly lands, and then flies off at ~12 s in the direction from which it arrived. While briefly perched, one can even see its tiny saddle on the trunk. The Red-headed Woodpecker is identified by its small size, and the dorsal wing surfaces of the wings show a black leading edge to the wing with extensive white, but the white is continuous from wing-to-wing because of the presence of the prominent white rump. Beginning at 32 s two putative Ivorybilled Woodpeckers enter the frame from the mid-right margin.
These two birds, clearly interacting, display field marks consistent with Ivory-billed Woodpeckers, including the dorsal wing surfaces of the putative Ivorybill with extensive white divided by a prominent black body, and a black leading edge to the wing (Video 9).

A PPE N D I X 10
Drone video clip filmed at our Louisiana study site depicting the landing of a Pileated Woodpecker on an upright snag. Here, the Pileated Woodpecker displays a very small amount of white on the dorsal surface of the wings compared to the putative Ivory-billed Woodpecker in Appendices 6 and 7, or the Red-headed Woodpecker in Appendix 12. An image extracted from this drone video clip also appears in Figure 10 (Video 10).

V I D E O 9 V I D E O 1 0 A PPE N D I X 11
A zoomed and cropped, three-quarters speed video shot of the two putative Ivory-billed Woodpeckers interacting in Appendix 9 (Video 11).

A PPE N D I X 12
Drone video clip filmed at our Louisiana study site depicting the landing of a Red-headed Woodpecker on an upright snag. Here, the Red-headed Woodpecker shows a black leading edge to the wing with extensive white, but the white is continuous from wing-to-wing because of the presence of the prominent white rump. Compare with the similar landing sequence of a putative Ivory-billed Woodpecker in Appendices 6 and 7, where the bird shows extensive white divided by a prominent black body, and a black leading edge to the wing. An image extracted from this drone video clip also appears in Figure 10 (Video 12).